1. Field of Invention
The invention relates to a method for a forming stepped structure in a multi-layer film stack on a substrate.
2. Description of Related Art
Advanced integrated circuits and memory devices incorporate stepped structures formed in multi-layer film stacks. Using dry pattern etching techniques, including plasma etch processes, a mask pattern is extended into the multi-layer film stack to form the stepped structure.
For example, a conventional method for preparing a stepped structure is illustrated in FIG. 1. The conventional method includes a process sequence 100 beginning with preparing a multi-layer film stack, including alternating first layers (125A, 125B) and second layers (120A, 120B) formed on or above substrate 110. A mask layer 130 having mask pattern 131 formed therein is prepared on or above the multi-layer film stack.
In 101A, the mask pattern 131 is transferred to the underlying first layer 125A using a first etch process to form a first layer pattern 121. Immediately thereafter, in 102A, the mask pattern 131 is further transferred to the underlying second layer 120A using a second etch process. Once the mask pattern is extended into the first layer 125A and the second layer 120A, the mask pattern 131 in mask layer 130 is trimmed in 103A to expose another portion 145 of the multi-layer film stack. However, the second etching process is known to alter or passivate an exposed surface 140 of mask layer 130, thus, interfering with the subsequent trimming of mask layer 130.
In 101B, 102B, and 103B, the first and second etch processes are repeated to form a stepped structure 150 including first step 152 and second step 154. However, as noted above, the second etching process adversely affects the trimming of mask layer 130, thus, making the trimming of mask layer 130 deficient and causing a degradation of the stepped structure formation in subsequent cycles. As a result, the ability to produce a stepped structure having multiple, well-defined steps may be severely limited, and, in extreme circumstances, the conventional method fails.